Embodiments of the present invention relate generally to the balancing of the thrust exerted in a centrifugal compressor, and more particularly to improving the maximum thrust that the architecture of a centrifugal compressor can withstand.
In operation, the rotor of a centrifugal compressor is generally subjected to significant thrusts. These thrusts are due to the pressure difference prevailing between the stages and to the quantity of movement created by the change of direction of the gas, from an axial direction to a radial direction. The flow rate tends to generate a thrust directed from the suction to the discharge of the compressor. The pressure difference at the limits of each wheel thrusts in the opposite direction.
The compensation of such a phenomenon is generally carried out by using a balancing piston which acts in the same direction as the thrust due to the flow rate. Bearing in mind that the compressor is likely to operate in various conditions, the piston is designed to reduce the thrust field across the entire operating range. A thrust bearing is installed to counter the residual thrust which remains despite the balancing implemented by the piston.
In certain specific cases of compressors, such as, for example, compressors with a wide flow rate range, that is to say with a high flow rate coefficient, the thrust bearing is not sufficient. To overcome this failing, it is known practice to place a control valve on the balancing line, that is to say between the rear cavity of the piston and the suction of the compressor. The valve is controlled by a thrust measurement probe, and regulates the pressure in the rear cavity of the piston. The thrust is therefore cancelled or at least reduced to keep it within the capability of the thrust bearing.
To avoid gas leaks that can damage the bearings or the dynamic seals when the control valve is closed and the rear cavity is pressurized, a suction chamber is arranged after the rear cavity of the piston via a labyrinth seal, and coupled via a suction pipe to the suction line at the output of the control valve.
However, this solution does not make it possible to compensate the thrust in the case of high gas flow rate. In practice, even with the control valve closed on the balancing line, it is not possible to reach the discharge pressure in the rear cavity of the piston, which results in a limiting of the thrust compensation.